The purpose of the CuDOSIS study is to examine the diagnostic value of activated macrophage imaging in patients with or under evaluation for cardiac sarcoidosis. The PET/CT tracer 64Cu-DOTATATE is used as a tool to identify activated macrophages. The trial is an open-label prospective study. The study will include 54 participants from the Department of Cardiology and the Department of Clinical Physiology, Nuclear Medicine, and PET at Rigshospitalet. Further, the study will include data from 22 patients with NET who have been scanned with 64Cu-DOTATATE PET/CT previously as negative controls. Participants will be included in the following groups: Group A: 22 patients with clinically suspected cardiac sarcoidosis Group B: 22 patients with known cardiac sarcoidosis Group C: Up to 10 patients with clinically suspected or confirmed acute lymphocytic myocarditis Group D: 22 patients with NET without known inflammatory heart disease who have previously been scanned with 64Cu-DOTATATE PET/CT as part of their routine diagnostic work-up or follow-up (control group)